Glucose modulation of memory storage processing

Epinephrine, derived from the adrenal medulla, enhances memory storage for several forms of learning. One physiological action of this hormone is to liberate hepatic glucose stores. This experiment tested the possibility that glucose could itself enhance memory. Rats were water deprived, pretrained to drink, pretrained to drink in the behavioral apparatus, and then trained in a one-trial inhibitory (passive) avoidance task. Immediately after the training footshock, the animals each received an injection of glucose (1.0-500 mg/kg). When tested for retention 24 h later, the animals which received 10 or 100 mg/kg doses of glucose exhibited enhanced retention performance; higher and lower doses had no significant effect on the memory tests. Also, glucose injections (100 mg/kg) delayed by 1 h after training had no effect on the retention tests. These findings suggest that the increase in plasma glucose levels subsequent to epinephrine injection may contribute to the effects of epinephrine on memory. In addition, the results suggest that peripheral glucose levels may exert important influences on memory storage.